Prefabricated wooden roof trusses are more economical and much faster to construct than a conventional or "stick framed" roof structure. However, when prefabricated trusses are installed and receive loads, internal web members under compression can sometimes buckle, resulting in a possible truss failure.
To prevent web members from buckling, the on-site addition of permanent web bracing is required by industry standards. The purposes of bracing are to hold the vertical position of the truss, maintain the design spacing of the truss, and reduce the buckling length of web members under a compression load. Such bracing may be continuous lateral, "T" bracing or other specialized methods. When four or more like trusses are installed in parallel, continuous lateral bracing is generally specified to brace designated web members. The lateral bracing, in turn, is secured by permanent diagonal bracing or anchorage to a solid end wall or other means to prevent any instability. "T"-bracing is specified when less than four parallel-like trusses or web-like members are adjacent. Such bracing may be conventional lumber, such as a 2.times.4, that may be an 80% portion of the length of a designated web length. Multi-ply girder or widely spaced trusses require specialized bracing methods. In addition, top chord and vertical members in a wood truss may require lateral bracing or sheathing. Multiple bearing trusses or cantilever conditions may require bottom chord members which have compression forces that require bracing.
The above-referenced supplemental lateral or "T" bracing is specified by the truss designer. Moreover, such bracing of the prior art is furnished and installed at the job site by the builder/framer after the trusses are erected. On-site installation of web bracing, however, is complicated, costly, and time consuming. Further, often on-site web bracing is sometimes installed incorrectly and sometimes inadvertently omitted. When installing bracing on site (see prior art bracing in FIG. 1), conventional lumber must be taken to the truss webs and either nailed across the mid-points of the appropriate webs members with the beams anchored at the ends or secured by a diagonal brace, or "T" bracing is installed along each web.
Inspection of on-site bracing is being more closely scrutinized, with the result that builders are requesting the truss fabricator itself to inspect each building after installation of the trusses for proper bracing. Even though truss fabricators are the most capable inspectors, they find this an impossible burden. For example, in a typical multi-family (apartment) project, approximately 8,000 roof trusses may be used having 12,000 webs that require bracing.
The use of the "pre-braced" compression web of a wood truss of the instant invention will satisfy the requirements for structural integrity of installed prefabricated wood trusses while eliminating the need for compression web bracing at the job site. The instant invention promises to reduce construction time and costs and provide a more accurately braced roof system.
To eliminate having to install bracing at a job site, the instant invention teaches hardware for prefabricated wood trusses which may be attached to wood web members under compression which require bracing. Such bracing may be installed while a truss is being fabricated. Hence, inspection of the compression web bracing at the job site will not be required, as with prior art continuous lateral and/or "T" bracing. The hardware for pre-braced wood trusses is designed to reinforce truss web members to be placed in compression and prevent buckling when the truss receives a load. The hardware for pre-braced compression web of a wood truss is preferably made of metal and most preferably made of galvanized steel. The attached drawings show several embodiments of the possible designs and attachment means for the hardware for the pre-braced wood trusses of this invention. In addition, a range of lengths and various gauges of steel may be used for the hardware.